The present invention relates to thermal packaging assemblies for any items which are to be packed in a thermally controlled environment for extended periods of time, such as foodstuffs, beverages, plants, other biological materials, medicines or other chemicals, temperature sensitive electronic equipment, tissue specimens, and so on.
The use of refrigerants to keep items or products cool over extended periods of time is widespread, both for transportation of heat sensitive or heat damageable products and for long term storage of such products. Refrigerators and refrigerated transport systems can be used on the large scale for storage and transportation, but less massive and expensive coolant systems are required for smaller scale purposes, for example short haul delivery systems, airline transportation, and home and recreational cooling of foods, beverages and the like.
The packing of temperature sensitive products such as foodstuffs, pharmaceuticals, plants, biological materials and the like in ice or dry ice to maintain their temperature over a prolonged period of time is well known and has been used extensively for many years. For example, the general public widely uses insulated containers or cool boxes packed with ice to maintain foodstuffs and beverages cool when camping, travelling or on picnics and the like. Commercially, ice is used in packing foodstuffs, flowers, plants and the like for transportation and storage until sold or until placed in a refrigerator in a store, for example. In the medical field, ice is used to reduce trauma, swelling and pain from injuries of all kinds, and is also used in transportation and storage of blood, tissue, organs, pharmaceuticals and the like. Ice or dry ice is also used in transport and use of heat sensitive equipment or instruments, and ice baths and controlled chemical reactions.
The use of ice or dry ice as a coolant material serves as a preservative in many cases and inhibits the growth of many harmful micro organisms. Another coolant in common use, particularly in cool boxes used for recreational purposes, is the so called "blue ice", which is a block or bag of coolant material which is frozen solid before being placed in a container such as a cool box to maintain foodstuffs or drinks in the container cool for extended periods of time.
The major drawback to the use of ice as a coolant material is that it melts. The space taken up by the ice when melted will be less than when it is frozen, so that it will no longer be an effective packing material. The melted ice is easily contaminated by microorganisms and, since it will be in intimate contact with the products it is protecting, these are also liable to become contaminated. They may also be damaged by getting wet. If the products to be protected cannot tolerate wetness, they must be protected from melted ice in some way, for example by the use of raised shelves in cool boxes for placing foodstuffs above the level of the ice or by some sort of waterproof packaging before they are packed in the ice. The melted ice will also allow the products to move or slosh around in the container, risking damage by impact with the walls of the container. The container itself must also be waterproof.
Dry ice has similar problems, in that it is converted into CO.sub.2 with time and thus the gas must be dissipated and the product will no longer be packed against movement in its container. Both water and dry ice can be used only once, adding to the expense of thermal storage.
In contrast, blue ice can be used repeatedly by refreezing the contents of the bag or block, but is brick hard when frozen into a solid block and is unable to conform to the shape of products to be kept cool in this state. Thus it does not maintain good contact with unevenly shaped products over a large portion of their surface area. It will become soft and pliable as the material melts within the bag.
Neither ice nor "blue ice" is shock absorbant when activated or frozen and they are therefore not ideal packaging materials, particularly of relatively fragile items or articles of complex and non uniform shapes.